Switching device having contacts

ABSTRACT

A switching device having moving contacts in a hermetically closed envelope with loose particles on the contact surfaces having a size of 0.01 - 10 Mu m of material having a specific resistance of &lt; 10 2 Omega cm in a quantity of at least 1 particle/sq.mm on a surface having a thickness of at least 1 Mu m and a hardness of at least 100 Vickers.

O Umted States Patent 1191 1 1 3,916,132

Steinmetz et al. Oct. 28, 1975 SWITCHING. DEVICE HAVING CONTACTS 2,121,180 6/1938 Vatter 200/267 x Inventors: Anthony Steinmetz e sum, 3,670,129 6/1972 Cherry et al 200/267 Netherlands; Hidde Walstra, OTHER PUBLICATIONS ,Attleboro1 Mass- Holms, Electrical Contacts Handbook, 1958 pp. [73] Assignee: U.S. Philips Corporation, New 3757-376- York, N.Y. Holms, Electrical Contacts, 1946, pp. 337338.

[22] Flled: May 1974 Primary Examiner-Robert K. Schaefer [21] Appl. No.: 466,714 Assistant ExaminerWilliam J. Smith Attorney, Agent, or Firm-Frank R. Trifari; Carl P. [30] Foreign Application Priority Data Stemhauser May 9, 1973 Netherlands 7306444 ABSTRACT 52 US. Cl 200/268; 200/279 A Switching device having moving Contacts in 3 [51] Int. Cl. H01H l/02 meticany closed envelope with loose Particles on the [58 Field of Search 200/267, 268, 269, 264, Contact Surfaces having a Size of 10111111 of mate- 200 279 239 rial having a specific resistance of 10 (2 cm in a quantity of at least 1 particle/sq.mm on a surface hav- [56] References Ci ing a thickness of at least 1 1111 and a hardness of at UNITED STATES PATENTS least 100 1,395,269 11/1921 Gebauer 200/267 x 2 Claims, No Drawings SWITCHING DEVICE HAVING CONTACTS Such devices using reed contacts in a miniaturized form in a hermetically closed envelope having a recent years frequently been used'in modern telephone exchanges, computer systems and data transmission systems.

In these switching devices the contacts members generally at the ends of resilient conductors are jointly present in a closed space filled with a shield gas. The conductors consist of magnetic material by which the contact can be opened or closed with the aid of coils or permanent magnets placed outside the envelope.

Very stringent requirements as regards lifetime both in the unloaded and the loaded condition are imposed on these devices while the contact resistance must be low and constant throughout the lifetime of the device.

It has been found that a considerably extension of the lifetime of contacts occurs when plane erosion can be brought about instead of the peak and crater erosion often becoming manifest. With plane erosion substantially the entire contact surface is used in contrast to only a small part in case of the peak and crater erosion. In addition in peak and crater erosion sticking of contacts often occurs. The extension of the lifetime is a factor of 100 or more when plane erosion occurs.

According to UK. Patent Specification No. 1,254,249 US. Pat. No. 3,663,777) in the name of the Applicant this can be realized in contacts having a contact coating which consists of at least two layers the outer one of which consists of metal having a thickness of 0.1 and 5 1.1.tm while immediately below or not immediately below this layer an interrupted or uninterrupted layer comprising at least 1 percent by volume of nonmetal is present.

This non-metal-containing layer may entirely consist of carbon, graphit, phosphorus, sulphur, silicon or metal oxide and may have a thickness of between 0.001 and atm and the outer layer consists of ruthenium and rhodium.

According to a further embodiment the non-metal is present in a finely divided form in a metal having a melting point of less that l500C in a total layer thickness of at least 0.] ,um.

The relevant layers on the contacts according to this patent application may be provided by cathodic sputtering of the relevant materials, by electrolytic coprecipitation, by vapour deposition or by electrophoresis,

thus by rather expensive techniques which make these devices rather expensive.

It was surprisingly found according to the invention that plane contact erosion can be realized in a simple manner in a contact device in a hermetically closed envelope filled with a shield gas, which device is characterized by the presence on the surface of the moving contacts of separate particles having a size of from 0.01 to pm of a material having a specific resistance of not more than 10 Qcm in a quantity of at least 1 particle per sq.mm while the surface of the contact members consists of metal having a thickness of at least 1 pm and a hardness of at least 100 Vickers.

A layer having a thickness of from 0.01 to 10 um consisting of metal having a specific resistance which is less that 10 Qcm is preferably present on the hard surface layer.

t, The-surprising effect isthatit is sufficient to have the relevant particles loosely on the contact surface .on

. which they remain; for the greaterpart due to weakadhesion'forces. Apparently they. aredisplaced'slightly on the-:contact surface and ensure that during switching This results in the desired plane erosion. The significance of the material choice of the surface the breakdown isvalways established at another layer of the contact members, that is to say, materials having a hardness of less than Vickers being excluded, is that the particles can remain stuck therein and in this manner can cause preferential breakdown. This becomes manifest in peak and crater erosion.

Thus according to the invention it is apparently essential that the particles remain mobile during the lifetime of the switching device.

According to another elaboration of the invention the particles in a method of manufacturing the switching device may be formed in a non-adherent manner on the surface of the contact members by effecting at their surface hydrolysis of chlorides which form compounds of the desired kind. As far as the size of the particles exceeds 10 am they are pulverized during the initial period by switching the switching device so that after a relatively small number of switching operations the required quantity of particles is formed.

EXAMPLES 1. Reed contacts are coated with a 3 ,um thick molybdenum layer by cathodic sputtering at a voltage of 1,500 V, a current intensity of 1.2 A and subsequently coated with a 0.1 pm thick layer of ruthenium at a voltage of 1,500 V and a current intensity of 0.4 A under an argon pressure of 10 mm Hg. Subsequently carbon particles are provided by immersion in a freon suspension. The reed contacts are subsequently sealed pairwise in a glass envelope and lifetested. This lifetest is effected in an unloaded condition and under the socalled crosspoint load in which cable discharges over 45, 75 and Ohm with cable lengths of 1, 2, 20 and 100 meters are performed under a direct voltage of 50 Volt. The contact coating exhibits in all these experiments a plane erosion and a low resistance of less that mOhm at at least 100 X 10 switching operations in the unloaded condition. The requirement of at least 0.5 3 X 10 switching operations in a loaded condition is easily satisfied.

2. Reed contacts are coated in the same manner as in example 1 with a 0.1 pm thick gold layer and subsequently provided with ruthenium particles by immersion in a suspension of ruthenium powder in freon (particle size 0.l 1 am). The contacts sealed in an envelope equipped with these materials have properties which are equivalent to those of example 1.

3. Reed contacts whose parts to be sealed within the envelope is approximately 7 mm long and 0.5 mm wise and which consist of nickel iron are coated in a cathode sputtering device with a film of gold having a thickness of 0.1 pm. The argon pressure during sputtering is 10" mm Hg, the voltage is 1,500 V and the current is 0.5 A. Subsequently a loose layer of carbon particles is provided by immersion in a suspension of carbon particles in freon. This cantata: coating has plane erosion and a low resistance in case 0f loaded switching. The results obtained are also equivalent to those with the contacts of example 1.

What is claimed is:

am and a hardness of at least Vickers.

2. A switching device as claimed in claim 1, characterized in that a film having a thickness of 0.01 1.0 pm is present on the hard surface layer and that this layer consists of metal having a specific resistance which is less that 10 Qcm. 

1. A switching device having moving contacts in a hermetically closed envelope filled with a shield gas, characterized in that the surface of the moving contacts is provided with loose particles having a size of from 0.1 - 10 Mu of a material having a specific resistance of not more than 10 2 Omega cm in a quantity of at least 1 particle per sq.mm, while the surface of the contact members consists of metal having a thickness of at least 1 Mu m and a hardness of at least 100 Vickers.
 2. A switching device as claimed in claim 1, characterized in that a film having a thickness of 0.01 - 1.0 Mu m is present on the hard surface layer and that this layer consists of metal having a specific resistance which is less than 10 4 Omega cm. 